Ion exchange resins are used in nuclear power plants and other nuclear facilities particularly to purify the coolant and moderator systems. These resins are usually contaminated with high concentrations of radioactive isotopes which itself may have interesting applications in medicine, science and industry. However, at this time, the spent waste resins including the radioactive isotopes are disposed at high costs because an economically useful process is still missing to separate the radioactive isotopes from the spent ion exchange resins. In some cases, even a permanent disposal of the spent waste resins is not possible because the resins are contaminated with long-living radioactive isotopes such as C-14. Therefore, these resins must be stored on-site of the nuclear power plant.
A process for the segregation of the isotope C-14 from spent waste resins of nuclear power plants is disclosed in CA 1 250 378 A. According to this process, carbon-14 is removed from particulate ion exchange resin by contacting, preferably at 70° C., a bed of the resin with a stream of air enriched with carbon dioxide, while the particulate ion exchange resin is in contact with water to displace the carbon-14 as gaseous carbon dioxide, and then scrubbing the gaseous carbon dioxide with soluble salts of calcium or barium, e.g. calcium hydroxide and barium hydroxide, to form either calcium carbonate or barium carbonate as a stable, carbon-14 containing compound which may be immobilized in cement.
This method is very time consuming and the efficiency of regeneration with air is very low. Further, the separated carbon-14 isotope is diluted with carbon dioxide from the processing air and must be separated from this mixture, or the total mixture must be disposed as radioactive waste.
In a paper entitled “Processing nuclear waste for isotope production”, CHANG, F., et al., Waste Management, Vol. 1 (Proc. Int. Conf. Tucson, Ariz., 1991), Arizona Board of Regents, Phoenix, Ariz. (1991), pages 781-787, the authors also disclose a method for recovering the isotope C-14 from spent ion exchange resin. A similar process is disclosed in U.S. Pat. No. 5,289,468 A. The isotope C-14 is removed from the ion exchange resin by acid stripping with hydrochloric acid to form carbon dioxide, which is then converted to carbon monoxide by reduction with zinc. 14CO is enriched by laser selective dissociation or by cryogenic distillation, and the purified 14CO is oxidized to produce carbon dioxide. The gas is finally converted to barium carbonate. However, this process substantially increases the amount of radioactive waste and disposal costs because the hydrochloric acid is used in a large excess and must be removed from the process using anionic exchange resins which then must be disposed as radioactive waste.
WO 96/01478 A is directed to a method and device for the disposal of a cationic exchange resin contaminated with radioactive and inactive cations. In the regeneration process, non-radioactive cations other than bivalent cations are converted to anionic complexes using oxalic acid and are washed out of the resin. Specifically, Fe(II) cations are oxidized to Fe(III) cations using hydrogen peroxide. The Fe(III) cations are then converted to anionic complexes using oxalic acid, and separated from the cationic ion exchanger. The anionic complexes are then oxidized and decomposed by photochemical oxidation of oxalic acid. The non-radioactive cations are disposed. The partly discharged ion exchange resin still containing the bivalent radioactive cations is reused.
WO 03/082751 A1 relates to a method for decontaminating metallic components which were exposed to radioactivity. An acid solution is used to remove radioactive contamination from the metallic components. A purification loop is provided comprising an ion exchange cell having a compartment filled with an ion exchange resin and two electrodes. A decontamination solution is passed through the ion exchange resin. The electrodes are separated from the ion exchange resin by cation exchange membranes. When a voltage is applied across the electrodes, hydrogen ions replace the cations in the ion exchange resin, which in turn are deposited at the cathode and are thereby removed from the decontamination solution. The ion exchange resin is continuously regenerated.
U.S. Pat. No. 7,070,685 B2 discloses a method to remove radionuclides from polluted water. Radionuclides present in cationic form are adsorbed on a cation exchanger, while the metals and radionuclides present in anionic form are removed from the solution by electrochemical deposition.